Microwave processing unit for pavement recycling and asphalt pavement production

ABSTRACT

An asphalt plant for producing a high performance hot mix asphalt product, comprising: RAP material, emulsion added to the RAP, and low energy microwave heating system for processing the RAP emulsion mix.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and incorporates by referencethe following U.S. Provisional Patent Application Nos. 61/643,010 and61/643,046 filed on May 4, 2012, and is a continuation in part of andincorporates by reference U.S. patent application Ser. No. ______ filedon May 6, 2013.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is in the technical field of asphalt production.More particularly, the present invention relates to the use of microwaveenergy in the production of asphalt products.

2. Background

Prior art asphalt production plants have remained virtually unchangedfor decades (see FIG. 1). Asphalt cement and aggregate are combined in amixing facility where they are heated, proportioned, and mixed toproduce the desired paving mixture. Hot-mix asphalt (“HMA”) facilitiesmay be permanently located (also called “stationary” facilities), or itmay be portable and moved from job to job. Hot-mix facilities may beclassified as either a batch facility or a drum-mix facility; both canbe either stationary or portable. Batch-type hot-mixing facilities usedifferent size fractions of hot aggregate which are drawn inproportional amounts from storage bins to make up one batch for mixing.The combination of aggregates is dumped into a mixing chamber called apugmill. The hot liquid asphalt, which has also been weighed, is thenthoroughly mixed with the aggregate in the pugmill. After mixing, thematerial it is then emptied from the pugmill into trucks, storage silos,or surge bins. The drum-mixing process heats and blends the aggregateswith asphalt all at the same time in the drum mixer. Typically $500-$700or more of natural fuels are burned for every hour of production. Whenmixing is complete, the hot-mix is then transported to the paving siteand spread with a paving machine in a partially compacted layer to auniform and even surface layer. While still hot, the paving mixture isfurther compacted by heavy rolling machines to produce a smooth pavementsurface.

Heat used in the production of hot-mix asphalt is one of the maintargets in efforts to reduce the energy profile and environmental impactof such facilities. Prior art facilities consume large amounts of energyand produce substantial amounts of pollutants. In recent years thedevelopment of WMA or warm mix asphalt was developed as a solution, butthis solution suffers from a number of drawbacks. While hot-mix asphaltis produced at 350 to 400 degrees, WMA is produced at 300 degrees, whichstill requires enormous energy and produces only incrementally lesspollutants. While these mixes show slight promise more information isneeded to draw definitive conclusions regarding their effectiveness andperformance as pavemet, but WMA does not does not fundamentally solvethe underlying problems associated with asphalt production.

Another problem with current asphalt production, especially with hot-mixasphalt, is it is produced using very little recycled pavement material(“RAP”). As RAP is harvested from roadways or parking lots only a smallamount will be used in new HMA production. Current nationwide standardsshow new HMA to contain anywhere from 20% to 35% of RAP in the HMA mixdesign. In most cases higher amounts of RAP causes a decline in new HMAperformance. As the years go by RAP piles continue to grow faster thanmaterial can be utilized in HMA. In several regions RAP is used as basematerial for roadways.

Thus, a need exists for an improved asphalt product and method ofproducing asphalt that does not suffer from the drawbacks anddisadvantages of the prior art.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved apparatusand method for an asphalt plant for producing a high performance hot mixasphalt product, comprising, RAP material, emulsion added to the RAP,and low energy microwave heating system for processing the RAP emulsionmix. These and other objects of the present invention will becomeapparent to those skilled in the art upon reference to the followingspecification, drawings, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing of a prior art asphalt plant.

FIG. 2 is a depiction of the steps of a process of producing highperformance hot mix asphalt (“HMA”) in accordance with the presentinvention. The drawing on the left depicts recycled asphalt pavement(“RAP”) material (up to 100%) from roadways or parking lots; the drawingin the center depicts a sized and injected engineered emulsion, whichcan constitute about 5% of the product; and the drawing on the rightdepicts a fused high performance HMA.

FIG. 3 is a block flow diagram of LEAP Process.

FIG. 4 is a drawing of a portion of a microwave heating system used inaccordance with the present invention.

FIG. 5 is a floor plan.

FIG. 6 is a floor plan.

FIG. 7 is a rendering of a LEAP plant.

FIG. 8 is a floor plan.

FIG. 9 is a graph of LEAP Rut Test Results.

DETAILED DESCRIPTION OF THE INVENTION

The present invention comprises a plant for producing a low energyasphalt pavement, which utilizes tested and designed equipment having alow energy heating system using microwave technology and manufacturingprocess (“LEHS”) for using up to 100% recycled asphalt pavement (“RAP”)to convert it into high performance hot mix asphalt (“HMA”) that outperforms prior art asphalt products of any type. LEHS uses very littleenergy and generates virtually untraceable amounts of pollution whencompared to current existing methods of producing HMA.

In general the process comprises the steps shown in FIG. 2.

The process starts with RAP material recovered from roadways, parkinglots or other paved surfaces. The process can use varying amounts of RAPincluding up to 100% RAP, which allows for maximum reuse or recycling ofproduct. An emulsion is added to the product, as describe in more detailbelow, the emulsion can constitute about 5% of the product (orvariations therefrom). After processing as described below, a fused highperformance HMA product is produced.

The RAP raw used for production, and tested as described below, camefrom several different climatic zones of the United States andrepresented the multiple variations of pavement that are present in thefield. The injection process can use conventionally available engineeredasphalt emulsions at a rate of 4% to 8%. The finished material hasstrength characteristic twice that of the best HMA currently inproduction, and at least as much flexibility to resist cracking as withprior art HMA.

The production process utilizes a much smaller footprint than existingpavement HMA manufacturing plants. The production process utilizessubstantially less energy, reduces the processing temperatures, andproduces substantially less pollution, and unlike prior art asphaltproduction facilities these advantages allow the production facility tobe placed inside an enclosed building opening up better strategic plantplacement reducing trucking making the process and product moreeconomical. The facility, without the prior art environmental and otherproblems, can be located closer to the points of use of the product,which tend to be in densely populated areas that previously would not besuitable locations for an asphalt plant. Also, an enclosed plant canoperate in cold and inclement weather, which is not possible orpractical for outdoor facilities. In colder climates, the energy demandsneeded to heat the product and the use of open flames made it impossibleto operate indoors and extremely expensive to operate in cold weather;so much so that asphalt plants in colder climates close during thewinter. The present invention substantially eliminates these and otherproblems.

FIG. 3 describes the general flow of the process of producing HMA inaccord with the present invention. The steps thereof are describedherein below. The low energy asphalt production (“LEAP”) process of thepresent invention process involves RAP receiving, RAP sizing andengineered emulsion injection, ambient temperature I-RAP (RAP injectedwith emulsion) storage, processing through the low energy microwaveheating system (“LEHS”), and storage and shipping of the final HMAproduct.

The LEAP standard HMA mix design is based on weight, and is to utilizeabout between 4 to 8 percent emulsion, about between 96 to 92 percentRAP, and optional addition about 1 percent lime, corresponding to an 85tons per hour (“TPH”) RAP feed rate, 4.5 TPH of emulsion, and 0.9 TPH oflime. Incoming RAP can be stored inside or outside the facility. Storinginside prior to processing will reduce moisture content on the feedstockfrom approximately 4 to 7 percent moisture at the time of delivery tominimum quantities at the time of use. Excess water, if any, is drivenoff within the microwave heating section and does not impact the finalproduct quality.

RAP Receiving

LEAP receives RAP via end dump trucks through a truck sized garage dooropening in the side of the processing building; the incoming material ismoved with a front end loader, conveyor or similar device. RAP is piledin a corner of the building forming multiple connected piles designedpreferably for combined storage of approximately 20,000 tons ofmaterial. Incoming RAP is to be graded by source. LEAP intends toutilize RAP from highways or other public projects to the extentpractical to limit the amount of incoming aggregate that is outsidetypical HMA DOT specifications. Should it become necessary to utilizeRAP from multiple sources, LEAP intends to from multiple piles tofacilitate multiple mix designs.

RAP Grinding and Emulsion Blending

RAP is to be ground using nominal 250TPH throughput grinding andblending unit, which are commercially available from Nesbitt Contractingor Caterpillar Corporation, which is designed to size RAP to between oneand a-quarter inch and one-half inch size depending on final mix design.The crushing/injection unit includes a screen on the incoming RAP thatallows material of one and one half inch or less in size to enter thegrinding section. Oversized material that will not pass through theincoming screen is sent to a crushing section to be reduced in size andthen returned to the incoming screen. Water is added to the RAP prior togrinding to control dust and minimize heat generation within thegrinding machine. Output from the grinding section is sent to twoparallel pug mills, which have the ability to blend or inject up to twodifferent grades of the liquid engineered emulsion with the ground RAP.Solid and liquid material is blended within a pug mill using theopposing paddles on two parallel shafts; the paddles simultaneously mixthe material and push the mixture from the inlet to the outlet of themill. The RAP-emulsion blend, known as intermediate or injected RAP(“I-RAP”), is to be conveyed from the outlet and piled on either side ofthe crushing/injection unit, production is sized such that the I-RAPmaterial can be produced at approximately 3 times the rate of theheating process (described below). I-RAP can be stored at ambienttemperature for up to 8 weeks prior to processing into HMA.

Low Energy Heating System (LEHS)

LEAP utilizes a microwave heating system (shown in FIG. 4) to heat theI-RAP to a pre-specified temperature prior to delivery for silo storageand/or to paving contractors. This system, known by LEAP as the LowEnergy Heating System (“LEHS”), uses microwave energy of about 915 MHzto selectively heat the aggregate within the I-RAP, enabling LEAP toheat the mixture without degrading the asphalt cement within theemulsion. LEAP uses two parallel heating systems with a minimum of about300 kW to 800 kW, each with 45 to 75 TPH of capacity, to process theI-RAP. Each LEHS system includes a minimum of four microwave transmitterunits with a splitter/wave guide that directs microwave energy from eachtransmitter into two rotary head heating chambers, resulting in acombined eight chambers per system (16 heating chambers per facility).I-RAP is passed through the microwave heating chambers using a beltconveyor at an I-RAP depth of slightly greater than 3 inches.

The engineered emulsions designed for use with the LEHS are preferablycapable of insulating and protecting the remaining asphalt binderpresent in the RAP from the violent heating power of the microwaves. Inparticular, aged RAP normally has 2.4 to 4% asphaltene binder,asphaltines are present in asphalt and the ratio of desirable maltenesto asphaltenes decreases over time due to weathering and oxidationcausing the asphalt to become dry or brittle. High concentration ofasphaltene has heretofore limited the usefulness of RAP such that iteither cannot be used, can only be used in limited quantities resultingon an inferior dry brittle product, or the asphaltines can be burned offat temperature producing pollutants. LEAP can utilize up to 100% RAPbecause it can rejuvenate asphaltenes, or otherwise increase the rationof maltenes to asphaltenes resulting in a very high quality HMA product.The microwave transmitters have the ability to generate variable orconstant power and the degree of heating is to be controlled by LEAP byadjusting the power and conveyor belt speed to increase or reduce theexposure time of the I-RAP within the LEHS. By varying the intensity ofthe power within the chamber or series of chambers different HMA mixdesigns can be produced with different performance characteristics.

Various exemplary layouts for the LEAS/LEAP plant are shown in FIGS.5-8, and can accommodate up to two LEHS systems can be located in closeproximity within a plant.

LEAP HMA Performance Characteristics

LEAP HMA for has been tested in comparison to Superior PerformingAsphalt Pavements (“Superpave”) standard developed for the U.S.Department of Transposition, Federal Highway Commission and used for allpaving projects that are funded in a whole or in part by federal funds.The principal measurement used for the evaluation of HMA is the tensilestrength ratio (“TSR”) which is used to predict the durability of theHMA. Some southern states, notably Texas and Louisiana, have replacedthe TSR measurement with the Hamburg Rut Test measurement as HMA laid atelevated temperatures can become brittle. The following table shows theresults of testing performed on LEAP HMA against the foregoingstandards.

LEAP HMA Property Testing Results per AET, Jan. 12, 2013⁽¹⁾ (HMA Samplesfrom Dec. 20, 2012 and Jan. 9, 2013) LEAP at LEAP at LEAP at SuperpaveHMA 230° F. 220° F. 290° F. Property SPWEB340B⁽²⁾ No Lime With Lime WithLime Asphalt Cement or Emulsion 5.5 5.0 5.0  5.0 Content - % by weightTSR 80.9 73.8 75.5  83.4 Percent Air Voids 4.0 3.0 2.8  3.8 Hamburg RutTest - 12.5 8,500 N/a 19,000 20,000+⁽³⁾   millimeter depths BulkSpecific Gravity 2.438 2.356 2.358   2.356 Density, lb./ft³⁽⁴⁾ 152.1147.0 147.1 147.0 Maximum Specific Gravity 2.540 2.396 2.422   2.396 DryTensile Strength, psi⁽⁵⁾ 68.1 128.6 199.1 226.3 Soaked Tensile Strength,psi 55.1 94.9 150.3 188.8 ⁽¹⁾Engineering Testing Summary, CriusCorporation Asphalt Plant Air Emissions Engineering Test, Dec. 18, 2012,AET Project Number 14-01235 ⁽²⁾SPWEB340B is a Minnesota Department ofTransportation Superpave specification where “SP” indicates the gyratory(testing) design, “WE” indicates a wear mixture, “B” indicates <¾″aggregate, “3” indicates the traffic level, “40” indicates 4.0 percentdesign air void, and the “B” indicates the virgin asphalt cement bindergrade. ⁽³⁾Test halted at 20,000 cycles, the upper limit of the testablerange. ⁽⁴⁾Lb./ft³ = pounds per cubic foot ⁽⁵⁾Psi = pounds per squareinch.

The Superpave specification, and most derivative state specifications,do not permit the use of more than 25 to 50 percent RAP within the HMAmix design due to the inability of traditional batch and drum HMA plantsto sufficiently heat the aggregate within the RAP to temperaturesnecessary to meet the minimum TSR specifications without forming excesssmoke emissions and particulate matter which violates standard airpermits. The HMA produced using LEAP production process meets or exceedsthe min TSR specification for most states while using 100% RAP andproduces virtually zero emissions or particulate matter.

Minimum TSR for Select State DOT Specifications TSR (Minimum) States 85%MS (with 1% lime) 80% VA, OR, FL, AL, NM, OK, SD, IA, NY, GA, AR, MN 70%CA, NV, MO, CO 60% AZ Hamburg Rut Test TX, LA, UT

Several of the southern states have moved to the Hamburg Rut Test for amore robust measurement of durability of the HMA. Virgin asphalt cementhad two primary chemical components, asphaltenes and maltenes.Asphaltenes are hard materials that provide the mechanical strengthwhile maltenes are the oily fraction which functions as the stickycomponent in HMA. Maltenes oxidize with age or excess heat to formasphaltenes which causes the HMA to become hard and brittle. The aged orheat damaged HMA cracks under heavy loads causing failures of the roadsurface. The Hamburg Rut Test is performed using a wheel which passedover an HMA sample until the ensuing rut exceeds 12.5 millimeters indepth. Southern states, where summer paving temperatures can prematurelyage the HMA, have been transitioning to the Hamburg Rut Test as a proxymeasurement to ensure that the maltene fraction was not damaged duringapplication. This test is an important benchmark for LEAP HMA as theasphalt cement within RAP has been aged, and traditional HMA using RAPis excess of 25 percent had a proclivity to fail early due to therelative lack of maltenes.

The graph in FIG. 9 shows the results for testing of two variations ofthe LEAP HMA.

LEAP Rut Test results far surpass Rut Test results for the bestperforming HMA product s, especially when you consider the RAP used wasnever designed for loading anywhere near this level (tensile <60).

The Green line represents material that was heated to 220 degrees; thepurple line was heated to 290 degrees. Conventional Superpave HMA failsat 8500 passes, while the LEAP HMA exceeded 20,000 cycles in some caseswithout failure.

LEAP Emissions

Emission testing shown below was performed for particulate and volatileorganic carbon (“VOC”) testing of the exhaust from an indoor LEHS systeminside. The summary of which is included below.

-   Overview: Particulate and VOC air emission testing was conducted on    a pilot scale asphalt plant on Dec. 18, 2012. Particulate emission    testing was conducted according to EPA Method 5 and EPA Method 202.    VOC emission testing was conducted in adherence with EPA Method 25A    using a Total Hydrocarbon (THC) Analyzer. At the time of the    emission test, the pilot scale asphalt plant was producing 10    Tons/Hour of asphalt.    -   A federal regulation (NSPS Subpart 1) exists for particulate        matter for all Hot Mix Asphalt Plants (HMA). Currently, there is        not a federal regulatory limit for VOC; VOC emissions are        compared to the EPA emission factors in the table below.        Detailed test results can be found in Table 1 and Table 2 which        are attached to this document.

Emission Unit Tested Pollutant Test Result Federal Standard Cirus PilotScale Particulate ≦0.04 0.0006 Asphalt Plant as Matter Grains/DSCFGrains/DSCF Tested Cirus Asphalt Plant Particulate ≦0.04 0.005 (Scaledup 8 times) Matter Grains/DSCF Grains/DSCF EPA Emission Factor CirusPilot Scale VOC 0.440 0.026 Asphalt Plant as Lbs/Hr ^(a, b) Lbs/Hr ^(a)Tested ^(a) VOC is equivalent to the Total Hydrocarbons as Propane. ^(b)This number represents the EPA emission factor for VOC emissions for aDrum Mix HMA running on natural gas.

TABLE 1 Summary of Asphalt Plant Particulate Test Results CriusCorporation -- Plymouth, Minnesota AET #14-01235 Parameter Run #1 Run #2Run #3 Average Particulate Matter (PM) Results Date Dec. 18, 2012 Dec.18, 2012 Dec. 18, 2012 Run Time 9:28-10:28 11:43-12:42 13:28-14:28 StackTemperature, ° F. 62 71 70 68 Stack Oxygen, % 20.7 20.7 20.7 20.7 StackCarbon Dioxide, % 0.2 0.2 0.2 0.2 Moisture, % 2.3 3.0 2.1 2.5 Stack FlowRate, DSCFM 700 700 700 700 Isokinetic Variation, % 101.4 100.1 99.2100.2 Filterable Particulate Emission Results Particulate Concentration,grains/dscf: 0.0010 0.0004 0.0005 0.0006 Particulate Mass Rate, Lbs/Hr:0.0059 0.0025 0.0028 0.0037 Organic Condensibles Emission ResultsParticulate Concentration, grains/dscf: 0.0002 0.0003 0.0002 0.0002Particulate Mass Rate, Lbs/Hr: 0.0011 0.0016 0.0013 0.0013 InorganicCondensibles Emission Results Particulate Concentration, grains/dscf:0.0008 0.0008 0.0007 0.0008 Particulate Mass Rate, Lbs/Hr: 0.0050 0.00460.0042 0.0046 Filterable + Organic Condensibles Emission ResultsParticulate Concentration, grains/dscf: 0.0012 0.0007 0.0007 0.0008Particulate Mass Rate, Lbs/Hr: 0.0070 0.0041 0.0040 0.0050 TotalParticulate Emission Results Particulate Concentration, grains/dscf:0.0020 0.0014 0.0014 0.0016 Particulate Mass Rate, Lbs/Hr: 0.0119 0.00860.0082 0.0096

TABLE 2 Summary of Asphalt Plant VOC Emission Test Results CriusCorporation - Plymouth, Minnesota Dec. 18, 2012 - AET #14-01235 AirflowPPMv, Lbs/ PPMv, Lbs/ Exhaust Rate Ave As Hr As Ave As Hr As LocationSCFM Propane Propane Carbon Carbon Run #1 9:29-10:28 Asphalt Plant 7005.90 0.028 17.7 0.023 Oven Outlet Run #2 11:42-12:41 Asphalt Plant 7004.94 0.024 14.8 0.019 Oven Outlet Run #3 13:28-14:27 Asphalt Plant 7005.10 0.025 15.3 0.020 Oven Outlet AVERAGES RUNS # 1-3 Asphalt Plant 7005.31 0.026 15.9 0.021 Oven Outlet

The pollution testing results indicate the LEAP plant will fall wellbelow the required emission standards for HMA production. These resultsdemonstrate that the LEAP plants are suitable for locations that areoutside the reach of conventional HMA plants in most states due topollution and air quality regulations.

LEAP Technologies plants can be placed in almost any industrial zoningthat supports trucking traffic. This significantly increases thecompetitive advantage over conventional asphalt plants by going wherethey cannot. Heretofore HMA plants, due to pollution and emissionissues, had to be located remotely, and typically not near locationswhere the HMA product is used. This greatly increased cost associatedwith product use because the product has to be transported greaterdistances than in possible with LEAP plants.

Furthermore, because LEAP plants can be located indoors and have muchreduced energy needs they can be operated year round in colder climatesand at much lower operating costs. Strategic locations will reducehauling rates and improve the economic impact to the end users.

Still further, LEAP plants have a much smaller footprint thanconventional asphalt plants, providing even greater advantages.

LEAP plants can be operated at the same time or operated based onproduct demand. Unlike existing conventional HMA plants there is littleeffort to engage production, simply turn on a few switches and yourproduction ready. The ease of production engagement allows ability tohave material readily available 12 months a year, even in northernclimates. Existing HMA plants in the northern regions are required toshut down during the winter months due to the high operational costs andrequired placement outdoors.

In the southern states or warmer climates the configurations shown belowallows for the RAP to be stored outside. LEAP plants can be locatedwithin a city in a facility of 40,000 sq. ft. or larger. By bringing theentire production process inside you retain the ability to produceanytime without the high cold weather start-up costs associated withconventional HMA plants.

While the foregoing written description of the invention enables one ofordinary skill to make and use what is considered presently to be thebest mode thereof, those of ordinary skill will understand andappreciate the existence of variations, combinations, and equivalents ofthe specific embodiment, method, and examples herein. The inventionshould therefore not be limited by the above described embodiment,method, and examples, but by all embodiments and methods within thescope and spirit of the invention. For example, the LEAS system could beused to modify existing asphalt plants to allow them to either reducethe level of pollution, by reducing the heat necessary, and/or toincrease the amount of RAP used in the creation of HMA to perhaps ashigh as about 70% to 80%.

1. An asphalt plant for producing a high performance hot mix asphaltproduct, comprising: RAP material; emulsion added to the RAP; low energymicrowave heating system for processing the RAP emulsion mix.